Biden is doing similar duty Tuesday with House Democrats, further putting his stamp on the agreement designed to avert the so-called "fiscal cliff" of tax hikes and budget cuts.

One of his jobs: Allaying some Democratic concerns that the proposal does not go far enough in terms of taxing the wealthy, and does nothing to address a looming battle over raising the debt ceiling.

The vice president's entry into talks signaled the endgame for the fiscal cliff deal, and it came at the behest of another old Senate colleague: Republican leader Mitch McConnell.

Saying he needed a "dance partner," McConnell said he called Biden into the talks on Sunday. The GOP leader and the Democratic vice president spoke by phone late into Sunday night and early Monday morning.

Biden served a bridge between McConnell and Obama, who have been critical of each other public and appear to have a somewhat frosty relationship.

The vice president remains a member in good standing of the Senate club. Not only did he serve as a senator from Delaware from 1973 until his election in 2008, his job as vice president also makes him president of the Senate (he actually votes in case of ties).

His relationships include McConnell, the top Senate Republican; Biden probably has the best entree to the GOP leader of anyone in the White House. The vice president once gave a speech at the McConnell Center at the University of Louisville.

As the Senate prepared to approve the fiscal cliff deal early Tuesday, McConnell credited Biden for "stepping up to play a crucial role."

Obama has also given Biden wide authority during his presidency. The vice president got involved in fiscal cliff negotiations in the midst of another major assignment: Developing proposals to address gun violence in the wake of the Connecticut elementary school shooting last month.

Now Biden will try to work his charms on House Democrats, seeking to nail down the fiscal cliff deal.